The invention relates to clutch discs or clutch plates of the type serving to transmit, or to interrupt the transmission of, torque between driving and driven rotary units, e.g., in friction clutches which are installed in the power trains of motor vehicles to transmit torque between a prime mover and a variable-speed transmission or between a transmission and a unit (such as a differential) which receives torque from the transmission.
A standard clutch plate or clutch disc (hereinafter called clutch disc) comprises a rotary support having a hub which can be non-rotatably mounted on the input shaft of a torque receiving unit (e.g., a transmission), and two annular friction linings which are affixed to the support and can be clamped between two coaxial rotary members (e.g., an axially movable pressure plate and an axially fixed counterpressure plate, such as a flywheel affixed to the output element of the internal combustion engine of a motor vehicle). The clutch can further comprise a so-called resilient cushion which is installed between the friction linings to yield during engagement and to dissipate energy during disengagement of the clutch.
Clutch discs of the above outlined character are disclosed, for example, in published German patent application Serial No. 30 23 634, in German Auslegeschrift No. 26 41 379, in German patent No. 27 20 664, and in U.S. Pat. Nos. 2,296,515 and 5,085,307.
When a friction clutch employing or cooperating with a clutch disc of the above outlined character is being engaged, the pressure plate is moved axially toward the counterpressure plate so that the two plates frictionally engage the adjacent exposed surfaces of the respective friction linings. At the same time, the two friction linings are caused to move axially toward each other and thus compress the resilient cushion between them. This entails a gradual (smooth) engagement of the clutch. During the initial stage of engagement of the clutch, the pressure plate and the counterpressure plate slip relative to the respective friction linings with attendant generation of friction heat, i.e., the temperature of the entire friction clutch rises. A serious drawback of such temperature change is that the conicity of the pressure plate increases or that the originally flat friction surface of the pressure plate assumes a conical shape. In fact, even the counterpressure plate (flywheel) of the clutch disc is likely to assume a conical shape which is undesirable even if it is less pronounced than the aforediscussed heat-induced conicity of the friction surface of the pressure plate.
The development of conicity at the friction surfaces of the pressure plate and counterpressure plate (also called reaction plate) results in the establishment of radially outwardly widening annular gaps between the two plates and the adjacent exposed surfaces of the respective friction linings. Reference may be had to the disclosure of U.S. Pat. No. 2,902,130. The development of such gaps, in turn, results in an unequal distribution of surface pressures upon the friction linings, as seen radially of the clutch disc, namely the surface pressure rises in a direction toward the axis of the clutch disc and decreases radially outwardly. Otherwise stated, the clutch disc exhibits a tendency to shift the effect of surface friction nearer to its axis. The result is a non-uniform wear upon the friction surfaces of the friction linings and a reduction of the maximal torque which can be transmitted by the clutch disc and the friction clutch embodying such clutch disc. The reason is a shift of the average effective friction diameter as a function of the radial distribution of surface pressure.
The only presently known solution of the above outlined problems is a replacement of the friction linings, a replacement of the clutch disc which employs such friction linings, or a replacement of the friction clutch which employs or cooperates with the clutch disc.